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Tuesday, October 07, 2008

A Safer Test for Down Syndrome

Continued from page 1

By Anna Davison

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Quake and his colleagues took blood samples from pregnant women who were considered at high risk of carrying a baby with aneuploidy and used high-throughput sequencing to amplify fragments of DNA from both the mother and fetus and to map its chromosomes. They then looked at the amount of material from each chromosome. An overabundance of any particular chromosome pointed to a genetic disorder. The results, Quake says, "can be as precise as you want simply by sequencing more fragments."

"It's a step forward," adds James Egan, chairman of the Department of Obstetrics and Gynecology at the University of Connecticut Health Center. "It has great potential, but it's not ready for prime time yet." Egan did not contribute to the Stanford study. Quake's team is now planning a larger study of several hundred pregnant women.

The cost of the sequencing used in the study was $700 per sample, but Quake says that it has since slipped to $300, as the cost of the technology continues to drop. "If it truly can be performed for $700, it could revolutionize the field," Simpson says.

Quake's team tested women in their second trimester of pregnancy, although he believes that the test could be used as early as 10 weeks into a pregnancy. A first-trimester test for Down syndrome would be preferable, so that parents have more time to decide if they wish to terminate the pregnancy, or to prepare for the birth of a baby with the disorder.

Quake's method is one of several different approaches to the problem of using fetal DNA in a noninvasive diagnostic test for genetic disorders like Down syndrome.

Sequenom, based in San Diego, is developing a test based on genes on chromosome 21 that code for fetal-specific RNA. Those markers can be used to count copies of the chromosome."There are thousands of genetic disorders that can easily be diagnosed with genetic screening," says Ravinder Dhallan, founder and CEO of Ravgen, a Columbia, MD-based biotech company that's developing diagnostic tests using fetal DNA. "Some are treatable today and many more may be treatable in the future.

It's not yet clear which method--or methods--will ultimately pay off. "It's like CDs or DVDs or thumb drives," says the University of Connecticut's Egan. "They're all different ways of approaching a problem. One or all will catch the imagination of the medical community and become a very useful clinical tool."

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Comments

  • People with Down syndrome are human beings...
    antibody on 10/07/2008 at 9:31 AM
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    As a father of a wonderful 9 year old son who happens to have Down syndrome, I was appalled by the statement "A first-trimester test for Down syndrome would be preferable, so that parents have more time to decide if they wish to terminate the pregnancy..." 

    Why is there the automatic assumption that parents would want to destroy their child just because he or she has a disability?  Are we that uncivilized? Or are we just ignorant of the wonderful qualities exhibited by people with this disability?

    Rather than spending all this money and brain power on how to detect birth defects earlier, why don't we instead focus on discovering what causes birth defects in the first place.  Those resources could also be used to develop better therapies and treatments for those among us who have disabilities.

    This weekend in every major metro area around the US friends and families are conducting various "Buddy Walks" to raise awareness of what Down syndrome really is. I challenge everyone on this forum to go spend a couple of hours educating yourself on all of the positive aspects of this disability. (Google: DS Buddy Walk and your area)
    Rate this comment: 12345
    • Re: People with Down syndrome are human beings...
      phoenix on 10/07/2008 at 11:37 AM
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      It would seem to be a more ethical approach than that of infanticide, where deformed or sickly newborns were simply left somewhere to die, which was a fairly common practice in some parts of Africa and other remote sections of the world right up until the middle of the 20th century. And many of those individuals deemed unworthy by the standards of Hitlers third reich, standards which were developed largely from the observations of Sir Francis Galton, the so called father of Eugenics, were sterilized so that they would not be able to reproduce. The option of terminating such a pregnancy, which you feel is unworthy of society even to contemplate, just might save a hopelessly deformed child from being brought into a world that would treat it as just another Elephant Man sideshow. 
      Rate this comment: 12345
    • Re: People with Down syndrome are human beings...
      Biologist on 10/08/2008 at 4:08 AM
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      antibody, the key phrase here is "parents have more time to decide if they wish to terminate the pregnancy". Emphasis is on the parents making this decision for themselves. There is absolutely no assumption that the parents would want to destroy their child. They have the choice of whether to take this test or not. When they receive the result, they then have the choice of what to do with that result.
      I work in this area, and routinely sign out results which parents use to make these choices, but when my wife was pregnant, we decided we would not terminate the pregnancy if Down syndrome was picked up on screening. It's all about choices.
      Rate this comment: 12345
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